Method and device for non-circular contour milling with a conical grinding wheel

ABSTRACT

Described is a method for the cutting machining of non-circular contours using a tool in the shape of a cone or a truncated cone positioned on a spindle for rotation, said spindle aligned at a certain angle with the workpiece axis on which the workpiece with the contour is positioned, whereby the tool is swiveled during the machining about at least one first swivel axis that is different from the spindle axis. Alternatively, the workpiece can be moved correspondingly, and the tool may remain unchanged in its alignment. Tool and workpiece also may undergo a corresponding movement together, since the crucial factor is solely the relative movement between tool and workpiece. Also described is a device for performing the method.

DESCRIPTION

1. Related Applications

This application is a US National Stage Application pursuant to 35 USC§371 based on the International Application PCT/EP99/02112, filed Mar.25, 1999, which in turn claims the priority of the German Application DE198 13 165.8, filed Mar. 25, 1998.

2. Field of the Invention

The invention relates to a method and a device for the cutting machiningof non-circular internal and external contours, for example camprofiles.

BACKGROUND OF THE INVENTION

Known methods of this type use a conical grinding wheel that is carriedby a spindle positioned at a certain angle in relation to the workpiece.This procedure has the advantage that, in particular for long workpiecessuch as camshafts, the grinding spindle can be constructed with a short,and thus rigid, design. If a grinding wheel in the shape of the cone ortruncated cone is used, it must, however, be ensured that the surfaceline of the grinding surface on the wheel that engages with theworkpiece is parallel to the desired surface; otherwise, the desiredsurface cannot be created, and a distortion of the surface occursinstead.

It is not a problem for dynamically balanced (circular) surfaces to beground because the grinding wheel must only be aligned accordingly inrelation to the workpiece. But for dynamically unbalanced (non-circular)surfaces, this is not possible with a stationary alignment of thegrinding wheel in relation to the workpiece.

DE 196 20 813 A1 and WO 97/44159 therefore introduce a method forgrinding cams in which the truncated cone-shaped grinding wheel is movedup and down on a Y axis in relation to the workpiece in order to ensurea corresponding alignment in relation to the workpiece. In this respect,reference is made to FIG. 4 of these documents.

When machining the displayed cam, a stationary alignment of the grindingwheel according to the unbroken line would cause the grinding zone onthe grinding wheel to be shifted between points A and B due to thenon-circular cam contour. Since the surface line of the grinding surfaceat the points above and below the axis, that is, also on points A and B,is not parallel to the desired surface, an unwanted distortion of theground surface would occur in this area.

To prevent this distortion, the mentioned documents provide that thegrinding wheel is moved along the Y axis, for example into the positionindicated by the broken lines. Although this does prevent a distortion,it was found that for certain contours no satisfactory grinding resultcan be obtained in this manner.

SUMMARY OF THE INVENTION

The invention is based on the task of creating a method, as well as adevice for the cutting machining of non-circular internal and externalcontours, which ensures a high machining quality.

This objective is realized by the characteristics of Claims 1 and 2, or13 and 14 respectively.

The invention is based on the idea of realizing this objective with acontinuous relative movement between tool and workpiece and achieving asatisfactory machining result. In the process, the inventors found thatan optimum result can be obtained with a swivel movement, since thisswiveling of the tool or workpiece results in a wobbling (or sweeping)movement, which again results in a high quality machining result, sinceno machining marks are created. Furthermore, in certain machining tasks,substantially better machine dynamics and a more favorable accelerationof the tool in relation to the workpiece can be achieved in this manner.

The invention creates a method for the cutting machining of non-circularcontours, such as cams, which uses a tool in the shape of a cone or atruncated cone, for example a grinding wheel, positioned on a spindlefor rotation, with said spindle aligned at a certain angle with theworkpiece axis on which the workpiece with the contour is positioned,whereby the tool is swiveled during the machining about at least onefirst swivel axis that is different from the spindle axis.

Since, naturally, the crucial factor here is solely the relativemovement between tool and workpiece, the workpiece can be movedaccordingly as an alternative. For this purpose, the tool is swiveledduring the machining about at least one first swivel axis that isdifferent from the workpiece axis.

Preferably, the first swivel axis is arranged parallel to the spindleaxis or workpiece axis at a certain distance. In addition, goodmachining results can be obtained if the tool or workpiece is swiveledduring machining also about a second swivel axis. Here also, the crucialfactor is solely the relative movement between tool and workpiece, sothat it is also possible to swivel the tool about one axis, and theworkpiece about another axis (sequentially or simultaneously).

In principle, very different orientations of the swivel axes areconceivable to achieve the desired effect and to keep the engagementline of the tool parallel to the desired surface. An orientation of thefirst swivel axis vertical to the spindle axis or the workpiece axis wasfound to be successful, whereby the second swivel axis stands verticalto the spindle axis or workpiece axis and also still vertical to thefirst swivel axis.

The first swivel axis is preferably located in the area of the tool orthe contour to be machined. Furthermore, it was found that a successfularrangement of the second swivel axis is located on the spindle axisbehind the first swivel axis when seen from the workpiece (10′ in FIG.2).

To increase the machining possibilities, the tool may be positioned sothat it can slide along the spindle axis, for example in a linearbearing. To adjust the machine to the actual machining task or to theparticular tool used, for example to the cone angle of a conicalgrinding wheel, the angle of the spindle axis may be adjustable inrelation to the workpiece axis.

It was also found to be advantageous if the workpiece can be machinedwith at least two tools while it is mounted. This means that whilegrinding a camshaft, a pre-grinding with a grinding disk that has arelatively large diameter is possible, for example, which is thenfollowed by a final grinding with a grinding wheel that has a smallerdiameter. For this purpose, the spindle head for positioning the spindlecan be swiveled to permit the engagement of another tool positioned onthe spindle head with the workpiece.

For camshafts, for example, angled or crowned contours of the cams maybe desirable. To achieve them, the tool may be provided with such asurface line. If necessary, the tool, as one example, a grinding wheel,can be adjusted accordingly. The invention is explained below in moredetail in reference to two exemplary embodiments.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a first exemplary embodiment of the invention.

FIG. 2 shows a second exemplary embodiment of the invention.

FIG. 3 shows a grinding wheel in the shape of a truncated cone that isengaged with a cam of a camshaft.

FIG. 4 shows a section through the cam and the grinding wheel with thetruncated cone shape.

DETAILED DESCRIPTION INCLUDING THE BEST MODES OF CARRYING OUT THEINVENTION

Next, reference is made to FIGS. 3 and 4 which show the basic machiningsituation, here in the form of a camshaft whose cams are ground with atruncated, cone-shaped grinding wheel. The camshaft 1 is positioned on aworkpiece axis 2 and has a cam 3 that should be ground using the showngrinding wheel 4. In order to obtain the desired cam contour—in thiscase the cam surface should be parallel to the workpiece axis 2 in thesection—the engagement line 5 of the mantle surface of the grindingwheel 4 must be aligned parallel with the workpiece axis 2. Thisalignment is ensured by angling the spindle axis 7 of the grinding wheel4 by an angle α. FIG. 3 shows an alignment of the grinding wheel 4 thatensures a distortion-free grinding of the upper cam part, but in whichit is not possible to grind the lower part without distortion in thisalignment, which is explained below. The cam 3 has a non-circulardesign, as seen in FIG. 4. During the grinding process, the engagementline 5 on the axis 6 is maintained in the lower concentric part of thecam 3. But when the upper, non-circular or non-concentric section of thecam 3 is ground, the engagement line, given an unchanged alignment ofthe grinding wheel 4, first shifts by an amount B upwards into position5B, and then downwards by an amount A below the axis 6 into position 5A.But, in positions 5A and 5B, the engagement line 5 of the truncatedcone-shaped grinding wheel 4 is not parallel to the desired cam surface,and this results in a deviation of the angle or a distortion of the camsurface. This distortion increases as the cone angle of the grindingwheel 4 increases.

To solve this problem, it is suggested by DE 196 20 813 A1 and WO97/44159 to move the grinding wheel 4 along the Y axis between thereturn points in positions 5A and 5B in such a way that the engagementline 5 is always on the axis 6 (as the cam rotates as shown by Arrow C).

According to the invention, the grinding wheel 4 or the spindle axis 7is swiveled during the grinding in relation to the angle position of thecamshaft 1 about a first swivel axis 8. By swiveling the spindle axis 7accordingly, the engagement line 5 of the grinding wheel 4, for example,can always be kept parallel to the workpiece axis 2. Naturally, acorresponding swiveling also can be used to intentionally achieve anon-parallel alignment, in order to, for example, achieve an angledgrinding of the cam surface, if necessary, over a certain area.

According to the second exemplary example, this is achieved by aswiveling of the spindle axis 7 about two axes, whereby the first swivelaxis 9 is vertical to the spindle axis 7, and the second swivel axis 10is vertical to the spindle axis 7 as well as to the first swivel axis 9.As shown, the second swivel axis 10 is located at a certain distancefrom the other axes.

In general, it is advantageous if in a design according to FIG. 2 thefirst swivel axis 9 is located in (or intersects) the area of either thesurface to be machined or the tool (i.e., it is close to the grindingwheel 4). The optimum design of the swivel axis depends on theparticular machining task and the machining tool. The selection of theaxes results in a specific relative movement between workpiece and tool,depending on the specific machining task, which again results in certainmachine dynamics. Since, in principle, the most continuous machiningprocess possible is desired without any major acceleration of the toolin relation to the workpiece, the optimal choice of the swivel axis orswivel axes depends on the machining task. But an optimization to thiseffect, using movement equations, is part of the tools of the expertresponsible for this (i.e., one of ordinary skill in the art) and neednot be explained in more detail.

In the described exemplary example, the grinding wheel is moved inrelation to the workpiece. Since the crucial factor is solely therelative movement between tool and workpiece, the workpiece can be movedin relation to the tool, as well, or both elements can be moved so thata corresponding relative movement is obtained.

PARTS LIST

This Parts List of the figure labels is for the convenience ofexamination, and may be canceled at the time of issuance.

α spindle axis angle relative to workpiece axis

B engagement line upward shift

A engagement line downwards shift

C workpiece rotation direction

1 workpiece shaft (e.g., camshaft)

2 workpiece axis (e.g., camshaft axis)

3 workpiece (e.g., cam)

4 tool (e.g., grinding wheel)

5 engagement line

5B engagement line upward position

5A engagement line downwards position

6 X axis (perpendicularly intersects the workpiece axis)

7 spindle axis (tool axis)

8 “first” first swivel axis (parallel to spindle or workpiece axis)

9 “alternative” first swivel axis (perpendicular to spindle or workpieceaxis)

10 second swivel axis (perpendicular to first swivel axis, andperpendicular to spindle axis or workpiece axis)

What is claimed is:
 1. In a method for the machining of non-circularcontours on a workpiece positioned on a workpiece axis, said method usesat least one tool in the shape of one of a cone or a truncated cone;said tool is positioned on a spindle for rotation, said spindel havingan axis, with said spindle axis aligned at a selected angle with saidworkpiece axis, the improvement comprising the step of: swiveling thetool relative to the workpiece during the machining about at least afirst swivel axis that is different from both the spindle axis and theworkpiece axis.
 2. The improved method as claimed in claim 1, wherein:the first swivel axis is arranged spaced a selected distance from andparallel to the spindle axis.
 3. The improved method as claimed in claim1, further comprising: the step of swiveling the tool relative to theworkpiece about a second swivel axis during machining.
 4. The improvedmethod as claimed in claim 3, wherein: a) the first swivel axis isperpendicular to the spindle axis; and b) the second swivel axis isperpendicular to both the first swivel axis and the spindle axis.
 5. Theimproved method as claimed in claim 3, wherein: the first swivel axisintersects the region defined by one of the tool and the contour beingmachined.
 6. The improved method as claimed in claim 3, wherein: thesecond swivel axis intersects the spindle axis behind the first swivelaxis as seen from the workpiece.
 7. The improved method as claimed inclaim 1, further comprising the step of: sliding the tool along thespindle axis.
 8. The improved method as claimed in claim 1, furthercomprising the step of: adjusting the angle of the spindle axis inrelation to the workpiece axis.
 9. The improved method as claimed inclaim 1, wherein: a) said at least one tool and said spindle aresupported and positioned by a spindle head, said spindle head includesat least a first tool and a second tool positioned thereon, and thespindle head can be swiveled to permit the engagement with the workpieceof said second tool positioned on the spindle head; and b) said methodincludes the step of swiveling said spindle head and engaging saidsecond tool with said workpiece.
 10. The improved method as claimed inclaim 1, further comprising the step of: adjusting said spindle angle sothat said spindle angle is different than the angle of said cone of saidtool shape in order to achieve an angled or crowned contour of saidworkpiece.
 11. The improved method as claimed in claim 1, wherein: a)said workpiece is a camshaft; and b) at least one of said tools is agrinding wheel.
 12. In a device for machining of non-circular contourson a workpiece positioned on a workpiece axis, said device includes atleast one tool in the shape of one of a cone and a truncated cone; saidtool is mounted on a spindle for rotation, said spindle having an axis,and said spindle axis is aligned at a selected angle with respect tosaid workpiece axis, said device includes a workpiece positioningmechanism and a spindle head for positioning said tool, the improvementcomprising: said spindle head includes a first swiveling mechanism forswiveling said tool so that during the machining the tool can beswiveled relative to the workpiece about a first swivel axis that isdifferent from both the spindle axis and the workpiece axis.
 13. Theimproved device as claimed in claim 12, wherein: the first swivel axisis arranged spaced a selected distance from and parallel to the spindleaxis.
 14. The improved device as claimed in claim 12, wherein: saidspindle head includes a second swiveling mechanism for swiveling saidtool so that the tool can be swiveled relative to the workpiece about asecond swivel axis during machining.
 15. The improved device as claimedin claim 14, wherein: a) the first swivel axis is perpendicular to thespindle axis; and b) the second swivel axis is perpendicular to both thefirst swivel axis and the spindle axis.
 16. The improved device asclaimed in claim 14, wherein: the first swivel axis intersects theregion defined by one of the tool and the contour to be machined. 17.The improved device as claimed in claim 12, wherein: the second swivelaxis intersects the spindle axis behind the first swivel axis as seenfrom the workpiece.
 18. The improved device as claimed in claim 12,wherein: said device includes a linear bearing mounting the tool so thatsaid tool is able to slide along the spindle axis.
 19. The improveddevice as claimed in claim 12, wherein: said device includes anadjustment mechanism permitting the adjustment of the angle of thespindle axis relative to the workpiece axis.
 20. The improved device asclaimed in claim 12, wherein: a) said device includes a spindle headsupporting and positioning said at least one tool, and said spindle headincludes at least a first tool and a second tool positioned thereon, andb) said device includes a spindle head swiveling mechanism permittingthe swiveling of the spindle head to permit the engagement of a selectedone of said first tool and said second tool with the workpiece.
 21. Theimproved device as claimed in claim 20, wherein: said first tool has alarger diameter than said second tool for pre-machining and said secondtool has a smaller diameter than said first tool for finishing.
 22. Theimproved device as claimed in claim 12, wherein: a) said workpiece is acamshaft; and b) said at least one tool is removably mounted on saidspindle so that said at least one tool can be retrofitted bysubstitution of a grinding wheel.